If the bars were vertical they were what is commonly considered as "breeding bars"
However, males too can get these bars. They don't acutally communicate breeding readiness per se but submission. The female shows them during spawning to show submission to the male.
When males get them it can be because they are scared.. not stressed per se but uncomfortable. I had a VT male once who had them for over a week after I bought him before he settled down. When my spawn was growing up I'd notice them from both males and females in the grow out tank if one was bullying another.
So... the short version is.. he probably was startled by your turning the lights on and that's what caused the stripes. Nothing to worry about.
Just for reference here's a picture of my man when he had his stripes...
And after he settled down.